Caption: Illustration showing the core, mantle and crust of Pluto. Observations by the hubble space telescope suggest that the internal composition of Pluto consists of roughly 50 to 70 percent rock and 30 to 50 percent ice by mass. The diameter of the core is thought to be about 70% of Pluto's diameter. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto's surface, leaving behind a dark, molasses-colored, carbon-rich residue. Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away.